The present invention relates in general to a driver circuit, and more particularly, to a driver circuit adapted for applying an AC drive voltage over preselected time intervals to a load circuit, such as a resistance heating element of an aroma generating apparatus and the like.
An aroma generating apparatus is a device adapted for long term use in generating preselected aromas from replaceable aroma producing material contained within a housing by means of an underlying heating element. One such apparatus is disclosed in Glucksman, U.S. Pat. No. 4,631,387. These aromas, such as perfumes, air fresheners, insecticide scents and the like, are sensed by the olfactory organs which are stimulated by relatively small quantities of gases or vapors in the air as low as one part per one million parts of air. The perception of smell by an individual is such, that if a given smell persists, the individual ceases to be aware of the smell for the individual makes an accommodation to the odor which is then treated as the prevailing environment. Thus, one who first enters an aromatic environment becomes immediately conscious of the odor, but the sensitivity thereto diminishes and virtually disappears if the individual remains in the environment. When, however, the individual leaves the aromatic environment and is exposed to the outside atmosphere, he quickly senses this change.
Thus, the operation of the human olfactory system is such that it is highly responsive to a change in the nature or level of an aroma but is desensitized when the prevailing odor attains a steady state condition. In a room having an aroma generating apparatus in which an aromatic vapor is continuously exuded, persons in the room subjected to the vapor cease in time to become aware of the aroma, even though it is continuously being produced, thus serving no useful purpose.
Accordingly, there is a need for a drive circuit for operating an aroma generating apparatus which functions to freshen or scent the air in a room in which the unit is placed, which unit will function to periodically discharge into the room atmosphere bursts of aromatic vapor, the non-aromatic intervals therebetween having a duration sufficient to avoid desensitizing the olfactory response of those exposed to the vapors. In Glucksman, a bimetallic element is incorporated within the drive circuit to energize and de-energize the heating element for predetermined durations to provide an aroma burst mode and an aroma maintenance mode. There is also known in Weiss, U.S. Pat. No. 4,492,880 a drive circuit for an electrically operated stapling device which incorporates an LM 555 integrated circuit timer which is operated as a one shot. The time period during which the integrated circuit timer remains on is greater than one-half, but less than one complete cycle of the input AC line voltage. As to these circuits, the Glucksman bimetallic element has the inherent disadvantages attributable to the mechanical action of the bimetallic element, while the Weiss drive circuit is of limited duration requiring the generation of triggering signals during the negative portion of the input AC line voltage cycle.